Lubricating oil composition

ABSTRACT

There is provided a lubricating oil composition that has good friction performance and friction performance durability, and which is unlikely to cause degradation of oil seals made from fluororubbers, and which is particularly useful as an automatic transmission fluid. This lubricating oil composition is produced by adding a phosphorus/nitrogen-containing ashless dispersant of 0.2 to 8 wt % with a nitrogen/phosphorus ratio of 1.5 to 2.8, a friction modifier of 0.01 to 5 wt %, a metal-containing detergent of 0.005 to 2 wt %, and an antioxidant of 0.1 to 5 wt % as additives to a base oil with a lubricating viscosity.

BACKGROUND OF THE INVENTION

The present invention relates to a lubricating oil composition, and more particularly relates to a lubricating oil composition that is very useful as an automatic transmission fluid.

DESCRIPTION OF THE RELATED ART

Lubricating oils, called automatic transmission fluids, have been used conventionally to assist smooth operation of automatic transmissions that are installed in automobiles and include a torque converter, a gear mechanism, a wet clutch, and a hydraulic mechanism. In modern automobiles, fuel economy has been increased, and reductions in size and weight have been attained in automatic transmissions as well. Accordingly, there is a need for automatic transmission fluids with even better friction characteristics and even better stability of these friction characteristics, that is, a reduction in variation in friction characteristics attributable to long-term use.

Japanese Laid-Open Patent Application 2003-321695 discloses an automobile transmission fluid that has a high coefficient of static friction and that is effective at buffering impacts that occur during shifting, wherein perbasic calcium sulfonate, a hydrocarbon-substituted succinimide, and a phosphorous acid ester compound are added to a lubricating base oil. It can be seen from the working examples in that an antioxidant is also added to the automobile transmission fluid that is prepared.

U.S. Pat. No 5,972,851 discloses a composition containing a dispersant and a friction modifier and having a total nitrogen-to-phosphorus weight ratio of approximately 3:1 to approximately 10:1 as an automobile transmission fluid that has good resistance to oscillation, high static torque, and superior resistance to friction.

With a device that needs lubrication, such as an automatic transmission or an automobile engine, oil seals or O-rings are used as sealing members to prevent the lubricating oil from leaking out. Many different materials have been used for these oil seals and O-rings, but as automatic transmissions, automobile engines, and the like have become smaller in recent years as mentioned above, there is a corresponding tendency for the temperature of the lubricating oil to rise in these devices, so fluororubbers, which have excellent heat resistance and also have high resistance to oil and chemicals, have come to be widely used as the material for oil seals and O-rings. However, these fluororubbers degrade in a relatively short time through contact with the nitrogen-containing dispersants that are generally contained in lubricating oils, and this is a problem in that the properties of the oil seals and O-rings end up being diminished within a relatively short time.

U.S. Pat. No. 4,615,826 and U.S. Pat. No. 4,747,971 disclose that a reaction product of fluorophosphoric acid and a perbasic nitrogen-containing dispersant is effective as a nitrogen-containing dispersant that is less likely to cause degradation of a fluororubber. Nevertheless, these patents are primarily aimed at developing an additive to be added to an engine oil, and therefore do not touch upon the friction characteristics of a lubricating oil composition to which this additive has been added.

U.S. Pat. No. 4,889,646 discloses that a lubricating oil composition containing a reaction product of a mineral acid such as sulfuric acid, nitric acid, or hydrochloric acid and a dispersant such as a viscosity index improver containing an amine dispersant, a Mannich dispersant, a succinimide dispersant, or a succinate ester amide dispersant, is effective as an engine lubricating oil that is unlikely to cause degradation of a fluororubber. Nevertheless, the invention described in this patent is aimed at developing an additive to be added to an engine oil, and therefore does not touch upon the friction characteristics of a lubricating oil composition to which this additive has been added.

U.S. Pat. No. 4,940,552 discloses that a reaction product of a dicarboxylic acid or an anhydride thereof and a dispersant having perbasic nitrogen is effective as a dispersant that is unlikely to cause degradation of a fluororubber. Nevertheless, the invention described in this patent is primarily aimed at developing an additive to be added to an engine oil, and therefore does not touch upon the friction characteristics of a lubricating oil composition to which this additive has been added.

DETAILED DESCRIPTION

An aspect of the present invention to provide a lubricating oil composition that can impart satisfactory friction characteristics, particularly to an automatic transmission, and which is less likely to cause modification of fluororubber sealing members. Thus, in part, it is directed to a lubricating oil composition, produced by adding a phosphorus/nitrogen-containing ashless dispersant of 0.2 to 8 wt % with a nitrogen to phosphorous mass ratio of 1.5 to 2.8, a friction modifier of 0.01 to 5 wt %, a metal-containing detergent of 0.005 to 2 wt %, and an antioxidant of 0.1 to 5 wt % as additives to a base oil with a lubricating viscosity (wherein the amounts in which the additives are added are in percentages with respect to the total weight of the lubricating oil composition).

The lubricating oil composition is a lubricating oil composition that can impart satisfactory friction characteristics and that is less likely to cause modification of fluororubber sealing members, so it is particularly useful as an automatic transmission fluid composition, demonstrating significant improvement of Viton Seal compatibility. Also, these superior characteristics are useful as a lubricating oil composition used to lubricate automobile engines and the like that are equipped with fluororubber sealing members, and therefore the lubricating oil composition of the present invention is useful as a lubricating oil composition in various different applications. Preferred embodiments of the lubricating oil composition of the present invention are listed below.

-   -   (1) The phosphorus/nitrogen-containing ashless dispersant is the         product of a reaction between a nitrogen-containing ashless         dispersant and phosphoric acid and/or phosphorous acid. The         phosphorus/nitrogen-containing ashless dispersant is non-borated         or essentially boron free meaning it has been post treated with         a boron component.     -   (2) The phosphorus/nitrogen-containing ashless dispersant is the         product of a reaction between polyisobutenylsuccinimide and         phosphoric acid and/or phosphorous acid.     -   (3) The polyisobutenylsuccinimide is a polyisobutenylsuccinimide         with a bis structure.     -   (4) The friction modifier is succinimide     -   (5) The succinimide is the product of a reaction between ammonia         and an alkenylsuccinic anhydride in which the alkenyl group is         an internal olefin obtained by the isomerization of an olefinic         double bond of a linear alpha olefin with 10 to 30 carbon atoms.     -   (6) The friction modifier is a fatty acid amide.     -   (7) The fatty acid amide is a reaction product obtained by a         condensation reaction of an amine and a monovalent fatty acid         with 6 to 30 carbon atoms.     -   (8) The friction modifier includes succinimide and a fatty acid         amide compound.     -   (9) The metal-containing detergent is an alkali metal sulfonate.     -   (10) The antioxidant is one or more ashless antioxidants         selected from the group consisting of amine compounds having an         antioxidant property, and phenol compounds having an antioxidant         property.     -   (11) The lubricating oil composition is used in an automatic         transmission.

Another aspect, is directed to an automatic transmission lubricating oil composition comprising 0.2 to 8 wt % of a phosphorolyated polyisobutenyl succinimide having a nitrogen/phosphorus mass ratio of 1.5 to 2.8 wherein the polyisobutenyl group has an average molecular weight of 900 to 2300; 0.01 to 5 wt % a friction modifier succinimide derived from the reaction product of an isomerized C₆ to C₃₀ alkenyl succinic anhydride with an amine selected from the group of ammonia, ethylenediamine, diethylenetriamine, triethylenetetramine, and tetraethylenepentamine; a metal-containing detergent of 0.005 to 2 wt %; and an antioxidant of 0.1 to 5 wt % as additives to a base oil with a lubricating viscosity, wherein the amounts in which the additives are added are in percentages with respect to the total weight of the lubricating oil composition. The automatic transmission lubricating oil demonstrates antiwear performance when the polyisobutenyl succinimide is employed in an amount to provide greater than about 200 parts per million phosphorous up to about 700 parts per million in the total lubricant. In one aspect, the automatic transmission lubricant can be essentially free of supplementary phosphorous containing additives. Many phosphorous compounds and anti-wear agents such as phosphate and phosphite, have harmful side effects on frictional properties, such as poor friction durability and poor anti-shudder durability. In this regard, another aspect is directed to a method for improving fluororubber seal compatibility while maintaining stability of the coefficient of friction as measured according to the JASCO M315:2004 in an automatic transmission comprising using an automatic transmission lubricating oil composition described herein above. Preferably the change in μd (%) is less than 10.

-   -   The base oil and additive components that constitute the         lubricating oil composition of the present invention will now be         described in detail.

Base Oil

There are no particular restrictions on the base oil in the lubricating oil composition of the present invention, and any of the lubricating base oils with various characteristics that have been used up to now as base oils for automobile engine (and especially gasoline engine) lubricating oil compositions or in automatic transmission fluids can be used. For example, Groups 1 to 3 mineral oils, Group 4 synthetic oils, and Group 5 base oils (base oils not encompassed by Groups 1 to 4) as set forth by ASTM can be used. It is preferable to use a mineral oil and/or synthetic oil containing at least 85 wt % (and preferably at least 90 wt %) saturated components, having a viscosity index of at least 110 (and preferably at least 120, and even more preferably at least 130), and having a sulfur content of no more than 0.01 wt % (and particularly no more than 0.001 wt %).

A mineral oil-based base oil preferably undergoes a suitable combination of treatments such as hydrogenation or solvent refining of a mineral oil-based lubricating oil fraction, and is particularly favorable to use a highly hydrogenated refined oil (also called a hydrocracked oil, which is typically an oil with a viscosity index of at least 120, an evaporation loss (ASTM D8500) of no more than 15 wt %, a sulfur content of no more than 0.001 wt %, and an aromatic content of no more than 10 wt %). Alternatively, a mixed oil containing at least 10 wt % of a hydrocracked oil such as this can also be used. These hydrocracked oils also encompass gas-to-liquid (GTL) base oils and oils with a high viscosity index (such as those with a viscosity index of at least 140, and particularly 140 to 150) and produced by an isomerization and hydrocracking process using as a raw material a synthetic wax made from natural gas or a mineral oil-based slack wax. Hydrocracked oils are preferable for the object of the present invention from the standpoints of low sulfur content, low volatility, low residual carbon content, and so forth.

Examples of synthetic oils (synthetic lubricating base oils) include poly-α-olefins that are C₃ to C₁₂ α-olefin polymer; dialkyl diesters that are esters of a C₄ to C₁₈ alcohol and a dibasic acid such as sebacic acid, azelaic acid, and adipic acid, which are typified by dioctyl sebacate; polyol esters that are esters of a C₃ to C₁₈ monobasic acid and 1-trimethylolpropane or pentaerythritol; and alkylbenzenes having a C₉ to C₄₀ alkyl group. In general, synthetic oils contain virtually no sulfur, have excellent oxidation stability and heat resistance, and when combusted produce little residual carbon or soot, which makes them preferable for the lubricating oil composition of the present invention. Poly-α-olefins are particularly favorable for the purposes of the present invention. Mineral oil-based base oils and synthetic base oils can each be used singly, but if desired, a combination of two more kinds of mineral oil-based base oil or two or more kinds of synthetic base oil can be used. Also, if desired, a mineral oil-based base oil and a synthetic base oil can be combined in any proportions.

Phosphorus/Nitrogen-Containing Ashless Dispersant with Nitrogen/Phosphorus Ratio of 1.5 to 2.8

The phosphorus/nitrogen-containing ashless dispersant with a nitrogen/phosphorus ratio of 1.5 to 2.8 contained in the lubricating oil composition of the present invention can be obtained as a uniform solution by mixing a nitrogen-containing ashless dispersant (usually containing approximately 60 wt % nitrogen-containing ashless dispersant (active components or solids) and approximately 40 wt % diluting mineral oil) and phosphoric acid or phosphorous acid in a proportion such that the nitrogen/phosphorus ratio will be from 1.5 to 2.8, and then stirring this mixture, usually for 0.1 to 5 hours, and usually between 40 and 200° C. (preferably between 50 and 150° C., and more preferably between 70 and 120° C.).

The preferable nitrogen/phosphorus ratio for use in the lubricating oil composition of the present invention is a range of 1.5 to 2.8, but more preferably the nitrogen/phosphorus ratio is no more than 2 5, and even more preferably this ratio is no more than 2.3, with a ratio of no more than 2.0 being particularly favorable. A phosphorus/nitrogen-containing ashless dispersant having a nitrogen/phosphorus ratio of 3 or higher will not exhibit a satisfactory effect in terms of suppressing the degradation of fluororubber.

Furthermore, the amount in which the phosphorus/nitrogen-containing ashless dispersant with a nitrogen/phosphorus ratio of 1.5 to 2.8 is contained in the lubricating oil composition of the present invention is preferably between 0.2 and 8 wt %, with a range of 0.5 to 5 wt % being even better. The amount in which this phosphorus/nitrogen-containing ashless dispersant is contained in the lubricating oil composition is preferably between 100 and 700 ppm calculated as total phosphorus content, with a range of 150 to 400 ppm being even better, and a range of 250 to 350 ppm being particularly favorable. In one aspect, the entire phosphorus content in the lubricating oil composition is derived from the phosphorus/nitrogen-containing ashless dispersant, thus the lubricating oil composition is essentially free of other phosphorous containing additives.

Typical examples of the nitrogen-containing ashless dispersant include alkenyl or alkyl succinimides derived from polyolefins, and derivatives thereof A succinimide can be obtained by a reaction between a succinic anhydride substituted with a high molecular weight alkenyl or alkyl group, and a polyalkylenepolyamine containing an average of 3 to 10 (and preferably 4 to 7) nitrogen atoms per molecule. The high molecular weight alkenyl or alkyl group is preferably a polyolefin with a number average molecular weight of approximately 900 to 5000, with polybutene being particularly favorable.

In some cases a chlorination method in which chlorine is used is utilized in the step of obtaining a polybutenyl succinic anhydride by a reaction between polybutene and maleic anhydride. With this method, however, although reactivity is good, a large amount of chlorine (such as about 2000 ppm) ends up remaining in the final succinimide product. On the other hand, if a thermal reaction is used in which no chlorine is involved, the amount of chlorine remaining in the final product can be kept to a very low level (such as 40 ppm or less). Also, compared to conventional polybutene (primarily one having a β-olefin structure), using highly reactive polybutene (one in which at least about 50% has a methyl vinylidene structure) is advantageous in that reactivity is increased even with a thermal reaction method. If reactivity is high, there will be less unreacted polybutene in the dispersant, so a dispersant with a high concentration of active component (succinimide) can be obtained. Therefore, it is preferable to manufacture a succinimide by first obtaining a polybutenyl succinic anhydride by thermal reaction using highly reactive polybutene, and then reacting this polybutenyl succinic anhydride with a polyamine. The succinimide can be used in the form of what is called a modified succinimide, by further reacting with boric acid, an alcohol, an aldehyde, a ketone, an alkylphenol, a cyclic carbonate, an organic acid, or the like. A boron-containing alkenyl (or alkyl) succinimide obtained by a reaction with boric acid or a boron compound is particularly advantageous in terms of thermal and oxidation stability. Succinimides come in mono, bis, and poly types, according to the number of imide structures per molecule, but bis types are preferable as the succinimide used for the purpose of the present invention.

Other examples of nitrogen-containing ashless dispersants include polymeric succinimide dispersants derived from an ethylene-α-olefin copolymer (such as one with a molecular weight of 1000 to 15,000), and alkenylbenzylamine-based ashless dispersants.

Particularly preferred nitrogen-containing ashless dispersants are mono and bis alkenyl succinimides derived from the reaction of alkenyl succinic acid or anhydride and alkylene polyamines. These compounds are generally considered to have the formula

wherein R¹ is a substantially hydrocarbon radical having a molecular weight from about 450 to 3000, that is, R¹ is a hydrocarbyl radical, preferably an alkenyl radical, containing about 30 to about 200 carbon atoms; Alk is an alkylene radical of 2 to 10, preferably 2 to 6, carbon atoms, R², R³, and R⁴ are selected from a C₁-C₄ alkyl or alkoxy or hydrogen, preferably hydrogen, and x is an integer from 0 to 10, preferably 0 to 3. The actual reaction product of alkylene or alkenylene succinic acid or anhydride and alkylene polyamine will comprise the mixture of compounds including succinamic acids and succinimides. However, it is customary to designate this reaction product as a succinimide of the described formula, since this will be a principal component of the mixture. The mono alkenyl succinimide and bis alkenyl succinimide produced may depend on the charge mole ratio of polyamine to succinic groups and the particular polyamine used. Charge mole ratios of polyamine to succinic groups of about 1:1 may produce predominately mono alkenyl succinimide Charge mole ratios of polyamine to succinic group of about 1:2 may produce predominately bis alkenyl succinimide

These N-substituted alkenyl succinimides can be prepared by reacting maleic anhydride with an olefinic hydrocarbon followed by reacting the resulting alkenyl succinic anhydride with the alkylene polyamine. The R¹ radical of the above formula, that is, the alkenyl radical, is preferably derived from a polymer prepared from an olefin monomer containing from 2 to 5 carbon atoms. Thus, the alkenyl radical is obtained by polymerizing an olefin containing from 2 to 5 carbon atoms to form a hydrocarbon having a molecular weight ranging from about 450 to 3000. Such olefin monomers are exemplified by ethylene, propylene, 1-butene, 2-butene, isobutene, and mixtures thereof.

In a preferred aspect, the alkenyl succinimide may be prepared by reacting a polyalkylene succinic anhydride with an alkylene polyamine. The polyalkylene succinic anhydride is the reaction product of a polyalkylene (preferably polyisobutene) with maleic anhydride. One can use conventional polyisobutene, or high methylvinylidene polyisobutene in the preparation of such polyalkylene succinic anhydrides. One can use thermal, chlorination, free radical, acid catalyzed, or any other process in this preparation. Examples of suitable polyalkylene succinic anhydrides are thermal PIBSA (polyisobutenyl succinic anhydride) described in U.S. Pat. No. 3,361,673; chlorination PIBSA described in U.S. Pat. No. 3,172,892; a mixture of thermal and chlorination PIBSA described in U.S. Pat. No. 3,912,764; high succinic ratio PIBSA described in U.S. Pat. No. 4,234,435; PolyPIBSA described in U.S. Pat. Nos. 5,112,507 and 5,175,225; high succinic ratio PolyPIBSA described in U.S. Pat. Nos. 5,565,528 and 5,616,668; free radical PIBSA described in U.S. Pat. Nos. 5,286,799, 5,319,030, and 5,625,004; PIBSA made from high methylvinylidene polybutene described in U.S. Pat. Nos. 4,152,499, 5,137,978, and 5,137,980; high succinic ratio PIBSA made from high methylvinylidene polybutene described in European Patent Application Publication No. EP 355 895; terpolymer PIBSA described in U.S. Pat. No. 5,792,729; sulfonic acid PIBSA described in U.S. Pat. No. 5,777,025 and European Patent Application Publication No. EP 542 380; and purified PIBSA described in U.S. Pat. No. 5,523,417 and European Patent Application Publication No. EP 602 863. The disclosures of each of these documents are incorporated herein by reference in their entirety. The polyalkylene succinic anhydride is preferably a polyisobutenyl succinic anhydride. In one preferred embodiment, the polyalkylene succinic anhydride is a polyisobutenyl succinic anhydride having a number average molecular weight of at least 450, more preferably at least 900 to about 3000 and still more preferably from at least about 900 to about 2300.

In another preferred embodiment, a mixture of polyalkylene succinic anhydrides are employed. In this embodiment, the mixture preferably comprises a low molecular weight polyalkylene succinic anhydride component and a high molecular weight polyalkylene succinic anhydride component. More preferably, the low molecular weight component has a number average molecular weight of from about 450 to below 1000 and the high molecular weight component has a number average molecular weight of from 1000 to about 3000. Still more preferably, both the low and high molecular weight components are polyisobutenyl succinic anhydrides. Alternatively, various molecular weights polyalkylene succinic anhydride components can be combined as a dispersant as well as a mixture of the other above referenced dispersants as identified above.

The polyalkylene succinic anhydride can also be incorporated with the detergent which is anticipated to improve stability and compatibility of the detergent mixture. When employed with the detergent it can comprise from 0.5 to 5 percent by weight of the detergent mixture and preferably from about 1.5 to 4 weight percent.

The preferred polyalkylene amines used to prepare the succinimides are of the formula:

wherein z is an integer of from 0 to 10 and Alk, R², R³, and R⁴ are as defined above. The alkylene amines include principally methylene amines, ethylene amines, butylene amines, propylene amines, pentylene amines, hexylene amines, heptylene amines, octylene amines, other polymethylene amines and also the cyclic and the higher homologs of such amines as piperazine and amino alkyl-substituted piperazines They are exemplified specifically by ethylene diamine, triethylene tetraamine, propylene diamine, decamethyl diamine, octamethylene diamine, diheptamethylene triamine, tripropylene tetraamine, tetraethylene pentamine, trimethylene diamine, pentaethylene hexamine, ditrimethylene triamine, 2-heptyl-3-(2-aminopropyl)-imidazoline,4-methyl imidazoline, N,N-dimethyl-1,3-propane diamine, 1,3-bis(2-aminoethyl)imidazoline, 1-(2-aminopropyl)-piperazine, 1,4-bis(2-aminoethyl)piperazine and 2-methyl-1-(2-aminobutyl)piperazine. Higher homologs such as are obtained by condensing two or more of the above-illustrated alkylene amines likewise are useful.

The ethylene amines are especially useful. They are described in some detail under the heading “Ethylene Amines” in Encyclopedia of Chemical Technology, Kirk-Othmer, Vol. 5, pp. 898-905 (Interscience Publishers, New York, 1950). The term “ethylene amine” is used in a generic sense to denote a class of polyamines conforming for the most part to the structure

H₂N(CH₂CH₂NH)_(a)H

wherein a is an integer from 1 to 10.

Thus, it includes, for example, ethylene diamine, diethylene triamine, triethylene tetraamine, tetraethylene pentamine, pentaethylene hexamine, and the like. The individual alkenyl succinimides used in the alkenyl succinimide composition of the present invention can be prepared by conventional processes, such as disclosed in U.S. Pat. Nos. 2,992,708; 3,018,250; 3,018,291; 3,024,237; 3,100,673; 3,172,892; 3,202,678; 3,219,666; 3,272,746; 3,361,673; 3,381,022; 3,912,764; 4,234,435; 4,612,132; 4,747,965; 5,112,507; 5,241,003; 5,266,186; 5,286,799; 5,319,030; 5,334,321; 5,356,552; 5,716,912, the disclosures of which are all hereby incorporated by reference in their entirety for all purposes.

Thereafter, the succinimide is reacted with a phosphorous source under suitable reaction conditions to provide a nitrogen to phosphorus mass ration of 1.5 to 2.8. Examples of inorganic phosphorous acids include phosphorous acid, hydrophosphoric acid, phosphorous trioxide, phosphorous tetraoxide and phosphoric anhydride. Partial or total sulfur analogs, such as phosphorotetrathioic acid, phosphoromonothioic acid, phosphorodithioic acid and phosphorotrithioic acid and P₂S₅ can be used. Particularly preferred is phosphorous acid. Specific examples of phosphoric acids are othophosphoric acid and metaphosphoric acid. Suitable procedures are for reacting a succinimide with a phosphorous source are set forth in U.S. Pat. Nos. 3,502,677 and 4,857,214, hereby incorporated by reference in their entirety for all purposes. In one aspect, the ashless dispersant is prepared by phosphorylating a succinimide, more particularly a polyisobutenyl succinimide, to such a degree that the nitrogen to phosphorous mass ratio in the reaction product is between about 1.5 to about 2.8; more preferably between about 1.5 to about 2.5; even more preferably between about 1.5 to about 2. In one aspect, the phosphorous/nitrogen containing ashless dispersant is substantially free of boron and thus, particularly preferred are phosphorylated polyisobutenyl succinimides substantially free of boron or non-borated phosphorylated polyisobutenyl succinimides.

Friction Modifier

A variety of known friction modifiers can be used as the friction modifier contained in the lubricating oil composition of the present invention, but a low molecular weight C₆ to C₃₀ hydrocarbon-substituted succinimide or a fatty acid amide is preferable. The friction modifier can be used singly or as a combination. The friction modifier is preferably contained in an amount of 0.01 to 5 wt % in the lubricating oil composition, and a range of 0.5 to 3 wt % is particularly favorable.

C₆ to C₃₀ Hydrocarbon-Substituted Succinimide

The friction modifying succinimide can be obtained by a reaction between ammonia or urea and a C₆ to C₃₀ hydrocarbon-substituted succinic acid or anhydride thereof The hydrocarbon-substituted succinic acid or anhydride thereof preferably has a C₆ to C₃₀ straight chain or branched chain alkyl or alkenyl group as a substituent. This hydrocarbon-substituted succinic acid can be obtained by a reaction between maleic anhydride and an olefin corresponding to the hydrocarbon substituent. A preferable olefin is a linear olefin with 10 to 30 carbon atoms, or an internal olefin obtained by isomerization of the double bonds of this olefin.

Particularly preferred succinimides are derived from isomerized alkenyl succinic anhydrides or their fully saturated alkyl analogs, suitable preparation methods are described in, for example U.S. Pat. No. 3,382,172. Commonly these materials are prepared by heating alpha-olefins with acidic catalysts to migrate the double bond to an internal position. This mixture of olefins (2-enes, 3-enes, etc.) is then thermally reacted with maleic anhydride. Typically olefins from C₆ (1-hexene) to C₃₀ (1-triacontene) are used. Suitable isomerized alkenyl succinic anhydrides include iso-decylsuccinic anhydride, iso-dodecylsuccinic anhydride, iso-tetradecylsuccnic anhydride, iso-hexadecylsuccinic anhydride, iso-octadecylsuccinic anhydride and iso-eicosylsuccinic anhydride. Preferred materials are iso-hexadecylsuccinic anhydride and iso-octadecylsuccinic anhydride. In another aspect, a C₆ to C₁₈ isomerized olefin is particularly favorable. The materials produced by this process contain one double bond (alkenyl group) in the alkyl chain. The alkenyl substituted succinic anhydrides may be easily converted to their saturated alkyl analogs by hydrogenation. The isomerized C₆ to C₃₀ alkenyl succinic anhydrides (or The isomerized C₆ to C₃₀ saturated-alkyl succinic anhydrides) can be reacted with amines to form the succinimide(s). Particularly preferred amines are ammonia, in another aspect the amine is a polyamine such as an ethylene amine Non-limiting examples include ethylenediamine, diethylenetriamine, triethylenetetramine, and tetraethylenepentamine and pentaethylene hexamine.

Other examples of favorable succinimides include a C₆ to C₁₂ straight chain hydrocarbon-substituted succinic acid or an anhydride thereof and a hydrocarbon-substituted succinic acid polyalkylenepolyaminoimide obtained by reacting a polyalkylenepolyamine in a molar ratio of (1.0 to 1.75):(0.25 to 1.0):1.0. Examples of polyalkylenepolyamines include ethylenediamine, diethylenetriamine, triethylenetetramine, and tetraethylenepentamine.

(2) Fatty Acid Amides

A fatty acid amide can be obtained by condensation between a C₆ to C₃₀ monovalent fatty acid and an amine The monovalent fatty acid is preferably a straight chain or branched chain, saturated or unsaturated monovalent fatty acid with 8 to 22 carbon atoms. Specific examples include octylic acid, lauric acid, myristic acid, palmitic acid, stearic acid, isostearic acid, oleic acid, and behenic acid. The amine can be a primary amine, secondary amine, ammonia, or polyalkylenepolyamine. The primary amine is preferably a C₈ to C₂₂ primary amine, specific examples of which include octylamine, decylamine, dodecylamine, tetradecylamine, hexadecylamine, octadecylamine, and oleylamine Specific examples of secondary amines include dioctylamine, didodecylamine, dioctadecylamine, and dioleylamine. Specific examples of polyalkylenepolyamines include ethylenediamine, diethylenetriamine, triethylenetetramine, and tetraethylenepentamine. Examples of particularly favorable fatty acid amides include an oleylamide obtained by a reaction between oleic acid and ammonia, and an amide compound obtained by condensation between 2 to 4 mol of isostearic acid and 1 mol of tetraethylenepentamine. This amide compound can also be used in combination with imidazoline.

Metal-Containing Detergent

There are no particular restrictions on the metal-containing detergent used in the lubricating oil composition of the present invention, but it is preferable to use a salt of an alkyltoluenesulfonic acid, alkylbenzenesulfonic acid, or petroleum sulfonic acid with a total base number of 10 to 500 mgKOH/g and an alkali metal (such as lithium) or alkaline earth metal (such as magnesium or calcium), or a perbasic compound thereof The metal-containing detergent can be used singly or in combination.

Also, an alkyl salicylate, alkyl carboxylate, and/or phenate of an alkali metal or alkaline earth metal can be used either singly or in combination with one of the above-mentioned sulfonates.

Antioxidant

It is preferable for the antioxidant to be at least one kind selected from the group consisting of phenol-based antioxidants and amine-based antioxidants known in the past. The antioxidant is preferably contained in the lubricating oil composition in an amount of 0.1 to 5 wt % (and particularly 0.5 to 3 wt %).

A hindered phenol compound is generally used as the phenol-based antioxidant, and a diarylamine compound is generally used as the amine-based antioxidant. Specific examples of hindered phenol antioxidants include 2,6-di-t-butyl-p-cresol, 4,4′-methylenebis(2,6-di-t-butylphenol), 4,4′-methylenebis(6-t-butyl-o-cresol), 4,4′-isopropylidenebis(2,6-di-t-butylphenol), 4,4′-bis(2,6-di-t-butylphenol), 2,2′-methylenebis(4-methyl-6-t-butylphenol), 4,4′-thiobis(2-methyl-6-t-butylphenol), 2,2-thio-diethylenebis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate], octyl 3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate, octadecyl 3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate, and octyl 3-(5-t-butyl-4-hydroxy-3-methylphenyl)propionate. Specific examples of diarylamine antioxidants include C₄ to C₉ mixed alkyldiphenylamines, p,p′-dioctyidiphenylamine, phenyl-α-naphthylamine, phenyl-β-naphthylamine, alkylated α-naphthylamines, and alkylated phenyl-α-naphthylamines. The hindered phenol antioxidants and diarylamine antioxidants can each be employed singly, or can be combined as desired. Other oil-soluble antioxidants may also be used together with these.

The lubricating oil composition of the present invention can further contain any of various known lubricating oil additives. Examples of these known lubricating oil additives include viscosity index improvers (such as dispersive and non-dispersive viscosity index improvers), corrosion inhibitors (such as thiazole compounds, triazole compounds, thiadiazole compounds, and other such copper corrosion inhibitors), antiwear agents (such as phosphoric esters, amine salts of phosphoric esters, phosphorous esters, amine salts of phosphorous esters, and thiophosphoric esters), seal expanders (such as oil-soluble dialkyl esters of adipic acid, azelaic acid, sebacic acid, phthalic acid, and other such dibasic acids), dyes (such as red dyes), antifoaming agents, and pour point depressants (such as polymethacrylic esters, polyacrylic esters, and polyacrylamides).

Working Examples Synthesis Example 1 Synthesis of Phosphorus/Nitrogen-Containing Ashless Dispersant (Dispersant A)

200 g of bis-type polyisobutenyl (PIB) succinimide (a solution containing approximately 40 wt % mineral oil; nitrogen content of solution: 2.0 wt %; number average molecular weight of PIB: approximately 1000, amine being a heavy polyamine comprising a mixture of largely tetraethylenepentamine and triethylenetetramine) was mixed with 5.3 g of phosphorous acid (phosphorus: 37.8 wt %). The mixture was stirred while the temperature was raised to 100° C., then held for 1 hour at this temperature, which gave a Dispersant A as the reaction product. This Dispersant A had a nitrogen content of 1.96 wt %, a phosphorus content of 0.97 wt %, and a nitrogen/phosphorus mass ratio of 2.0.

Synthesis Examples 2 to 7 Synthesis of Phosphorus/Nitrogen-Containing Ashless Dispersants (Dispersants B to G)

Using 200 g of the same bis-type polyisobutenyl (PIB) succinimide (a solution containing approximately 40 wt % mineral oil) as that used in Synthesis Example 1, Dispersants 2 to 7 were obtained by the same procedure as in Synthesis Example 1, except for using phosphorous acid in the amounts listed in Table 1. Table 1 also lists the nitrogen and phosphorus contents, and their content ratios, for Dispersants B to G thus obtained.

TABLE 1 Succinimide Phosphorous acid Reaction product amount used amount used Dispersant N (%) P (%) N/P Synthesis Example 1 200 g 5.3 g A 1.96 0.97 2.0 Synthesis Example 2 200 g 4.6 g B 1.96 0.85 2.3 Synthesis Example 3 200 g 4.3 g C 1.97 0.79 2.5 Synthesis Example 4 200 g 3.55 g  D 1.98 0.66 3.0 Synthesis Example 5 200 g 2.95 g  E 1.98 0.55 3.6 Synthesis Example 6 200 g 2.7 g F 1.98 0.5 4.0 Synthesis Example 7 200 g 1.1 g G 2.0 0.2 10.0

Synthesis Example 8 Synthesis of Friction Modifier (FM-1)

1000 g (2.84 mol) of isomerized octadecenyl succinic anhydride was put into a four-neck flask equipped with a stirrer, a thermometer, and a dehydrator, the inside of the flask was replaced with nitrogen while the contents were stirred, and the temperature was raised to 130° C. Ammonia was then poured in, the temperature was raised to 180° C., and ammonia was added for 6.5 hours until no more heat was generated. After this, the pressure was reduced to 50 Torr, and dehydration was performed for 1 hour. 995 g of a light brown, viscous liquid (nitrogen content of 3.85 wt %) was finally obtained as the reaction product (FM-1).

Synthesis Example 9 Synthesis of Friction Modifier (FM-2)

68.3 g (0.323 mol) of isomerized n-octenyl succinic anhydride and 130 g (0.107 mol) of polyisobutenyl-substituted succinic anhydride with a molecular weight of 1000 were put into a four-neck flask equipped with a stirrer, a thermometer, and a dehydrator, and the atmosphere was replaced with nitrogen while the temperature was raised to 90° C. 22.05 g (0.215 mol) of diethylenetriamine was then added dropwise. Upon completion of the dropping, the mixture was heated to 160° C., and the water that was produced was removed while the mixture was heated and stirred for 2 hours. After this, the reaction product was dehydrated for 1 hour at a temperature of 160° C. and a reduced pressure of 50 Torr. A light brown, viscous liquid (nitrogen content of 4.3 wt %) was finally obtained as the reaction product (FM-2).

Synthesis Example 10 Synthesis of Friction Modifier (FM-3)

180 g (0.61 mol) of isostearic acid was put into a four-neck flask equipped with a stirrer, a thermometer, and a dehydrator, and the atmosphere was replaced with nitrogen while the temperature was raised to 90° C. 36.7 g (0.194 mol) of tetraethylenepentamine was then added dropwise. Upon completion of the dropping, the mixture was heated to 213° C. over a period of 3 hours, and the reaction product was dehydrated for 5 hours at the same temperature and a reduced pressure of 50 Torr. A brown, viscous liquid (nitrogen content of 6.4 wt %) was finally obtained as the reaction product (FM-3).

Working Examples 1 to 4 and Comparative Examples 1 to 4 Manufacture of Lubricating Oil Composition

A phosphorus/nitrogen-containing ashless dispersant, a friction modifier, a metal-containing detergent, an antioxidant, a corrosion inhibitor, a viscosity index improver, and an antifoaming agent were added in the following amounts to a specific base oil to prepare lubricating oil compositions.

(1) Base Oil

A mixture of 42.69 weight parts of a base oil with a 100° C. kinematic viscosity of 3.5 mm²/s (belonging to Group 3) and 42.69 weight parts of a base oil with a 100° C. kinematic viscosity of 4.0 mm²/s (also belonging to Group 3).

(2) Phosphorus/Nitrogen-Containing Ashless Dispersant

3.0 weight parts (added amount of solution containing approximately 40% mineral oil) of the phosphorus/nitrogen-containing ashless dispersant listed in Table 2 (one of the Dispersants A to G synthesized in the synthesis examples given above).

(3) Friction Modifier

A mixture of 2.0 weight parts of the FM-1 or FM-2 listed in Table 2, and 0.25 weight part of FM-3.

(4) Metal-Containing Detergent 0.1 weight part (added amount of solution containing approximately 40% mineral oil) of perbasic calcium sulfonate with a total base number (TBN) of 315 mgKOH/g.

(5) Antioxidant

A mixture of 0.5 weight part of an amine-based antioxidant (an alkyldiphenylamine) and 0.5 weight part of a phenol-based antioxidant (a hindered phenol mixture).

(6) Corrosion Inhibitor

0.07 weight part of a thiazole corrosion inhibitor (an alkylthiadiazole).

(7) Viscosity Index Improver

8.20 weight part of non-dispersive polymethacrylate-based viscosity index improver.

(8) Antifoaming Agent

Silicone oil.

Evaluation of Lubricating Oil Composition

(1) Fluororubber Compatibility Test

F585, which is a standard material for a rotary oil seal made by NOK, was used as the fluororubber material. The test was conducted according to the method in JASO M344-92, in which a fluororubber piece was soaked for 72 hours at 150° C. in a lubricating oil composition, after which the change in elongation and the change in tensile strength were measured.

(2) Shell Four-Ball Wear Test

Using a Shell four-ball tester, the wear resistance was evaluated under test conditions comprising a load of 392 N, a rotational speed of 1200 rpm, a test oil temperature of 70° C., and a test duration of 1 hour. Wear resistance was evaluated by measuring the diameter of wear marks in the balls at the end of the test.

Evaluation Results for Lubricating Oil Composition

The results are given in Table 2 below.

TABLE 2 Working Example Comparative Example 1 2 3 4 1 2 3 4 Phosphorus/nitrogen-containing ashless dispersant A A B C D E F G N/P ratio 2.0 2.0 2.3 2.5 3.0 3.6 4.0 10.0 Friction modifier (FM-) 1 + 3 2 + 3 1 + 3 1 + 3 1 + 3 1 + 3 1 + 3 1 + 3 Fluororubber immersion test results Change in elongation (%) −9.5 −9.5 −11.6 −12.5 −16.1 −19.7 −20.1 −19.6 Change in tensile strength (%) −5.0 −5.0 −7.6 −9.2 −11.6 −14.8 −15.7 −18.3 Shell four-ball wear test results: wear mark diameter (mm) 0.48 0.46 0.49 0.53 0.58 0.70 — —

As reference examples, the fluororubber immersion test and the Shell four-ball wear test were also conducted on two kinds of commercially available automatic transmission fluid. As a result, with one of the commercially available automatic transmission fluids, the change in elongation was −12.4%, the change in tensile strength was −7.7%, and the wear mark diameter was 0.53 mm, and with the other commercially available automatic transmission fluid, the change in elongation was −4.5%, the change in tensile strength was −13.8%, and the wear mark diameter was 0.56 mm.

This confirms that the lubricating oil composition of the present invention makes it less likely that a fluororubber seal will deteriorate than with a lubricating oil composition containing a phosphorus/nitrogen-containing ashless dispersant with a nitrogen/phosphorus ratio of 3.0 or higher, and also contributes to improvement of the wear resistance of the machinery.

Working Example 5 and Comparative Examples 5 and 6

Manufacture of Lubricating Oil Composition

A combination of a phosphorus/nitrogen-containing ashless dispersant (3.0 weight parts of Dispersant A (an amount including approximately 40 wt % mineral oil)) or a nitrogen-containing ashless dispersant containing no phosphorus (3 weight parts (an amount including approximately 40 wt % mineral oil)) and a phosphorus-based friction modifier (0.18 weight part of butyl acid phosphate or dibutyl hydrogenphosphate), an organic friction modifier (FM-3: 2.0 weight parts), a metal-containing detergent (0.1 weight part of the calcium sulfonate used in Working Example 1 (an amount including approximately 40 wt % mineral oil)), an antioxidant (a combination of 0.5 weight part of the amine-based antioxidant and 0.5 weight part of the phenol-based antioxidant used in Working Example 1), a corrosion inhibitor 0.07 weight part of the thiadiazole-based inhibitor used in Working Example 1, a viscosity index improver (8.20 weight parts of the polymethacrylate-based non-dispersive viscosity index improver used in Working Example 1), and an antifoaming agent (0.002 weight part of the silicone oil used in Working Example 1) were added to the same base oil as that used in Working Example 1 (total: 85.38 weight parts) to prepare a lubricating oil composition.

Evaluation of Friction Stability of Lubricating Oil Composition

The stability of the coefficient of friction was measured according to the JASO M315:2004 automatic transmission fluid standards, in which the change (50 to 5000 cycles) in type 1 and type 2 dynamic friction coefficient (μd) is specified as 10% or less.

The measurement of pd by the following test was conducted by a dynamic friction test method using an SAE No. 2 tester, as set forth in the JASO M348:2002 automatic transmission fluid friction test method. The change in pd was calculated from the following equation, and was rounded off to the nearest integer.

Change in μd (%)=(maximum value−minimum value)−(maximum value)×100

Note: The maximum and minimum values are the maximum and minimum values between 50 and 5000 cycles.

The JASO M348:2002 automatic transmission fluid friction test method is summarized below:

(1) Friction Materials

Friction material: FZ127-24-Y12, steel plate: FZ132-8Y2

(2) Dynamic Friction Test Conditions

Inertial moment of inertial disk: 0.343 kg·m², oil temperature: 100° C.

(3) Recording of Dynamic Friction Coefficient

Test cycles: The dynamic friction coefficient (0) was recorded after 1, 5, 10, 20, 50, 100, 200, 500, 1000, 2000, 3000, 4000, and 5000 cycles.

Table 3 shows the results of evaluating friction stability.

TABLE 3 Working Comparative Comparative Example 5 Example 5 Example 6 Dispersant Dispersant A phosphorus-free dispersant Phosphorus-based — phosphate phosphate friction modifier N/P ratio 2.0 2.0 2.0 Friction stability Maximum value of μd 0.148 0.158 0.168 Minimum value of μd 0.137 0.138 0.142 Change in μd 7% 13% 26%

The lubricating oil composition pertaining to Working Example 5 of the present invention exhibited high stability of its dynamic friction coefficient (μd). 

1. A lubricating oil composition, produced by adding a phosphorus/nitrogen-containing ashless dispersant of 0.2 to 8 wt % with a nitrogen/phosphorus ratio of 1.5 to 2.8, a friction modifier of 0.01 to 5 wt %, a metal-containing detergent of 0.005 to 2 wt %, and an antioxidant of 0.1 to 5 wt % as additives to a base oil with a lubricating viscosity, wherein the amounts in which the additives are added are in percentages with respect to the total weight of the lubricating oil composition.
 2. The lubricating oil composition according to claim 1, wherein the phosphorus/nitrogen-containing ashless dispersant is the product of a reaction between a nitrogen-containing ashless dispersant and phosphoric acid or phosphorous acid and wherein the ashless dispersant is non-borated.
 3. The lubricating oil composition according to claim 1, wherein the phosphorus/nitrogen-containing ashless dispersant is the product of a reaction between polyisobutenylsuccinimide and phosphoric acid or phosphorous acid.
 4. The lubricating oil composition according to claim 3, wherein the polyisobutenylsuccinimide is a polyisobutenylsuccinimide with a bis structure.
 5. The lubricating oil composition according to claim 1, wherein the friction modifier is a C₆ to C₃₀ hydrocarbon substituted succinimide
 6. The lubricating oil composition according to claim 5, wherein the succinimide is the product of a reaction between ammonia and an alkenylsuccinic anhydride in which the alkenyl group is an internal olefin obtained by the isomerization of an olefinic double bond of a linear alpha olefin with 10 to 30 carbon atoms.
 7. The lubricating oil composition according to claim 1, wherein the friction modifier is a fatty acid amide.
 8. The lubricating oil composition according to claim 7, wherein the fatty acid amide is a reaction product obtained by a condensation reaction of an amine and a monovalent fatty acid with 6 to 30 carbon atoms.
 9. The lubricating oil composition according to claim 5, wherein the friction modifier includes succinimide and a fatty acid amide compound.
 10. The lubricating oil composition according to claim 1, wherein the metal-containing detergent is an alkali metal sulfonate.
 11. The lubricating oil composition according to claim 1, wherein the antioxidant is one or more ashless antioxidants selected from the group consisting of amine compounds having an antioxidant property, and phenol compounds having an antioxidant property.
 12. An automatic transmission lubricating oil composition comprising 0.2 to 8 wt % of a phosphorolyated polyisobutenyl succinimide having a nitrogen/phosphorus mass ratio of 1.5 to 2.8 wherein the polyisobutenyl group has an average molecular weight of 900 to 2300; 0.01 to 5 wt % a friction modifier succinimide derived from the reaction product of an isomerized C₆ to C₃₀ alkenyl succinic anhydride with an amine selected from the group of ammonia, ethylenediamine, diethylenetriamine, triethylenetetramine, and tetraethylenepentamine; a metal-containing detergent of 0.005 to 2 wt %; and an antioxidant of 0.1 to 5 wt % as additives to a base oil with a lubricating viscosity, wherein the amounts in which the additives are added are in percentages with respect to the total weight of the lubricating oil composition.
 13. The automatic transmission lubricating oil composition according to claim 12, wherein the phosphorolyated polyisobutenyl succinimide is non-borated.
 14. The automatic transmission lubricating oil composition according to claim 12 wherein the total phosphorous content in the lubricating oil composition is less than 700 parts per million phosphorous.
 15. A method for improving fluororubber seal compatibility while maintaining stability of the coefficient of friction as measured according to the JASCO M315:2004 in an automatic transmission comprising using an automatic transmission lubricating oil composition comprising 0.2 to 8 wt % of a phosphorolyated polyisobutenyl succinimide having a nitrogen/phosphorus mass ratio of 1.5 to 2.8 wherein the polyisobutenyl group has an average molecular weight of 900 to 2300; 0.01 to 5 wt % a friction modifier succinimide derived from the reaction product of an isomerized C₆ to C₃₀ alkenyl succinic anhydride with an amine selected from the group of ammonia, ethylenediamine, diethylenetriamine, triethylenetetramine, and tetraethylenepentamine; a metal-containing detergent of 0.005 to 2 wt %; and an antioxidant of 0.1 to 5 wt % as additives to a base oil with a lubricating viscosity, wherein the amounts in which the additives are added are in percentages with respect to the total weight of the lubricating oil composition. 